U.S. patent application number 10/213693 was filed with the patent office on 2004-02-12 for spin-forming method for making catalytic converter.
Invention is credited to Lanzesira, Joseph Michael, Li, Houliang, Nelson, Earl T..
Application Number | 20040025341 10/213693 |
Document ID | / |
Family ID | 27757384 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040025341 |
Kind Code |
A1 |
Li, Houliang ; et
al. |
February 12, 2004 |
SPIN-FORMING METHOD FOR MAKING CATALYTIC CONVERTER
Abstract
A method is provided for forming a catalytic converter
comprising a catalyst substrate having a noncircular circumference
and a metal housing disposed about the substrate. The catalyst
substrate is initially measured to determine the radial dimension
of the substrate circumference relative to a central axis. The
substrate is wrapped in a compressible mat and arranged within a
metal tube. The arrangement is subjected to a spin-forming process
that forms the metal tube about the catalyst substrate. The
spin-forming process includes rotating the metal tube about the
substrate axis, while concurrently urging a metal-forming tool
against the metal tube. The metal-forming tool is programmed to
follow a metal-forming path corresponding to the substrate
circumference plus a predetermined radial distance. In this manner,
a metal housing is formed having a noncircular circumference
corresponding in shape to the catalyst substrate and spaced apart
by a uniform insulative layer.
Inventors: |
Li, Houliang; (Novi, MI)
; Lanzesira, Joseph Michael; (Monroe, MI) ;
Nelson, Earl T.; (Livonia, MI) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60611
US
|
Family ID: |
27757384 |
Appl. No.: |
10/213693 |
Filed: |
August 6, 2002 |
Current U.S.
Class: |
29/890 |
Current CPC
Class: |
F01N 13/18 20130101;
B21D 22/14 20130101; B21D 53/88 20130101; F01N 2450/02 20130101;
F01N 3/2853 20130101; Y10T 29/49345 20150115; Y10T 29/49799
20150115; Y10T 29/49934 20150115; Y10T 29/49808 20150115; Y10T
29/49771 20150115 |
Class at
Publication: |
29/890 |
International
Class: |
B21D 051/16 |
Claims
1. A method for forming a catalytic converter comprising a catalyst
substrate having a substrate axis and a noncircular circumference
about the substrate axis, an insulative layer about the catalyst
substrate, and a metal housing disposed about the insulative layer,
said method comprising: measuring the catalyst substrate to
determine radial dimensions of the noncircular circumference
relative to the substrate axis, arranging the catalyst substrate
and a compressible mat within a metal tube such that the
compressible mat is interposed between the metal tube and the
catalyst substrate, and spin-forming the metal tube about the
catalyst substrate to form the metal housing and to compress the
compressible mat between the catalyst substrate and the metal
housing to form the insulative layer, said spin-forming comprising
rotating the metal tube about the substrate axis and concurrently
radially urging a metal-forming tool against the metal tube, said
spin-forming further comprising programming the metal-forming tool
to follow a metal-forming path corresponding to the radial
dimensions of the substrate circumference plus a predetermined
radial distance, thereby forming a metal housing having a
noncircular circumference corresponding in shape to the substrate
and spaced apart therefrom by the insulative layer.
2. A method according to claim 1 wherein the substrate has an oval
circumference.
3. A method according to claim 1 wherein the step of spin-forming
further comprises axially advancing the metal-forming tool while
radially urging the metal-forming tool against the metal tube to
progressively form the metal tube.
4. A method according to claim 1 wherein the metal-forming tool is
a roller rotatable about a roller axis parallel to the substrate
axis.
5. A method according to claim 1 wherein the catalyst substrate is
an out-of-round substrate having radial dimensions about the
substrate axis that vary depending upon direction.
6. A method for forming a catalytic converter comprising a catalyst
substrate, an insulative layer surrounding the catalyst substrate,
and a metal housing having a housing midsection surrounding the
catalyst substrate and the insulative layer, said method
comprising: providing a catalyst substrate having a substrate axis
and a noncircular substrate circumference about the axis, measuring
the noncircular substrate circumference, said measuring comprising
selecting a reference direction relative to the axis and
determining the radial dimensions to the circumference as a
function of angular displacement relative to the reference
direction, wrapping a compressible mat about the catalyst substrate
to from a wrapped substrate, providing a metal tube comprising a
tube midsection having a tube axis, coaxially inserting the wrapped
substrate into the midsection of the metal tube, and spin-forming
the metal tube about the wrapped substrate to form the housing
midsection, said spin-forming comprising rotating the metal tube
about the tube axis, and radially urging while axially advancing a
metal-forming roller against the metal tube to reduce the radial
dimensions and to compress the compressible mat to form the
insulative layer, said spin-forming further comprising positioning
the metal-forming roller a radial distance relative to the
substrate axis and adjusting the radial distance of the
metal-forming roller as a function of the angular displacement
relative to the reference direction, such that the metal-forming
tool is positioned a radial distance relative to the substrate axis
equal to the radial dimension of the substrate plus a predetermined
radial dimension, whereby the metal-forming roller forms the
housing midsection having a shape corresponding to the noncircular
circumference of the catalyst substrate and spaced apart therefrom
by an insulative layer having substantially uniform thickness.
7. A method according to claim 6 wherein the metal-forming roller
is rotatable about a roller axis parallel to the substrate
axis.
8. A method according to claim 6 wherein the catalyst substrate is
a out-of round cylindrical substrate.
9. A method according to claim 6 wherein the substrate has an oval
circumference.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to a method for manufacturing a
catalytic converter by spin-forming a metal tube about a catalyst
substrate to form a housing. More particularly, this invention
relates to a spin-forming method wherein the catalyst substrate has
a noncircular circumference and wherein the metal-forming tool is
positioned during spin-forming to form a housing shaped similar to
the catalyst substrate and sized greater than the catalyst
substrate by a uniform distance.
BACKGROUND OF THE INVENTION
[0002] Automotive vehicles are equipped with a catalytic converter
for treating exhaust gases to reduce noxious compounds prior to
emission into the atmosphere. A typical catalytic converter
comprises a catalyst substrate that is formed by extruding and
firing a ceramic material and defines a plurality of passages that
are coated with catalyst agents for treating exhaust gases caused
to flow therethrough. The catalyst substrate is generally
cylindrical and is enclosed in a metal housing. A thermally
insulative material is interposed between the catalyst substrate
and the metal housing to maintain the substrate at an elevated
temperature effective for treatment and prevent overheating of the
housing.
[0003] It has been proposed to manufacture a catalytic converter by
spin-forming a metal tube about the catalyst substrate to form the
housing. During spin-forming, the catalyst substrate is positioned
in the metal tube, and the substrate and tube are rotated about a
central axis. The metal forming tool is radially urged against the
metal, while advancing axially, to reduce the circumference of the
tube. Multiple passes are typically required in order to achieve
the desired product size and shape. For each pass, the tool is
radially advanced a small distance, so that the diameter is reduced
incrementally.
[0004] In conventional spin-forming processes, the metal-forming
tool is positioned a fixed distance from the axis, and produces a
housing having a circular cross section. Thus the process is suited
for producing a housing about a cylindrical substrate with a
circular cross-section uniformly spaced from the housing. It is
desired to produce a catalytic converter having other shapes, which
would need to be based upon a substrate having a noncircular
cross-section; for example, an oval circumference. Moreover, even
for catalyst substrates that are designed to be cylindrical, the
radial dimensions of the substrate tends to vary as a result of the
extruding and firing of the ceramic material, so that the
circumference of the catalyst substrate is not a true circle, but
tends to have a radius that varies with direction, a condition
referred to as out-of-round. During spin-forming, regions of the
substrate having a greater radius than specified may experience
higher pressure from the metal-forming tool, which may cause
breakage of the fragile substrate. Furthermore, variations in the
radius may result in a non-uniform thickness of insulation between
the substrate and the housing.
[0005] Therefore, a need exists for a method of forming a catalytic
converter by spin-forming that is suited for forming a metal
housing about a catalyst substrate having a noncircular
circumference, either by design or as a result of deviations that
occur during processing of the ceramic. It is desired that the
housing formed by spin-forming be spaced apart form the noncircular
substrate by a uniform radial distance, such that a uniform layer
of insulative material is disposed between the housing and
substrate.
BRIEF SUMMARY OF THE INVENTION
[0006] In accordance with this invention, a method is provided for
forming a catalytic converter that includes a catalyst substrate
having a noncircular circumference. The catalyst substrate is
measured to determine the radial dimension of the noncircular
circumference relative to an axis. The catalyst substrate is
wrapped in a compressible mat and arranged in a metal tube. The
arrangement is subjected to a spin-forming process that forms the
metal tube about the catalyst substrate into a metal housing. The
spin-forming process includes rotating the metal tube about the
substrate axis and concurrently radially urging a metal-forming
tool against the tube. In accordance with this invention, the
metal-forming tool is programmed to follow a metal-forming path
corresponding to the substrate circumference plus a predetermined
radial distance. In this manner, a metal housing for the catalytic
converter is produced having a noncircular circumference that
corresponds in shape to the substrate and is spaced apart therefrom
by an insulative layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The present invention will be further illustrated with
reference to the accompanying drawings wherein:
[0008] FIG. 1 is a cross-section of a catalyst substrate for
forming a catalytic converter in accordance with a preferred
embodiment of this invention;
[0009] FIG. 2 is a cross-sectional view showing an arrangement of
components for spin-forming a catalytic converter in accordance
with a preferred embodiment of this invention;
[0010] FIG. 3 is a cross-sectional view of the arrangement in FIG.
2 taken along lines 3-3 and looking in the direction of the
arrows;
[0011] FIG. 4 is a cross-sectional view of the arrangement in FIG.
2 showing the components during spin-forming of a catalytic
converter in accordance with this invention;
[0012] FIG. 5 is a cross-sectional view showing a catalytic
converter spin-formed in accordance with this invention;
[0013] FIG. 6 is a cross-sectional view of the catalytic converter
in FIG. 5 taken along the lines 6-6 in the direction of the
arrows;
[0014] FIG. 7 is a cross sectional view of a catalyst substrate
that is out-of-round for forming a catalytic converter in
accordance with an alternate embodiment of this invention; and
[0015] FIG. 8 is a cross-sectional view of a catalytic converter
comprising the catalyst substrate in FIG. 7 and spin-formed in
accordance with an alternate embodiment of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] In accordance with a preferred embodiment of this invention,
referring briefly to FIGS. 5 and 6, a method is provided for
manufacturing a catalytic converter 40 comprising a ceramic
catalyst substrate 10 having an oval circumference and enclosed
within a metal housing 42 spaced apart by a layer 43 of insulative
material. The method uses a spin-forming process, carried out using
a metal-forming tool 30 in FIG. 4, to form the metal housing having
a similar oval shape to the substrate and sized greater than the
substrate to provide a uniform layer of insulation
therebetween.
[0017] Referring to FIG. 1, in this embodiment, substrate 10 has an
axis 14 and an outer surface 18 characterized by an oval
circumference. Substrate 10 comprises end faces in FIG. 2 and
defines a plurality of axial passages between the ends, of which
only a few are depicted. The substrate is formed by extruding and
firing a ceramic material. During use, exhaust gas from an internal
combustion engine flows through passages 12 and is treated by
catalytic agents applied on the passage surfaces.
[0018] Prior to assembly, outer surface 18 of substrate 10 is
mapped to determine the radial dimensions relative to axis 14. For
this purpose, the dimensions are measured between axis 14 and a
series of points at the surface. The points are located in planes
perpendicular to the axis and equidistantly spaced about the
circumference. Thus, each point is readily identified by an angular
displacement relative to a reference direction 16 and an axial
distance relative to an end 15 of the substrate. Measurements may
be made by any suitable technique that provides an accurate
distance of a surface relative to a predetermined reference point,
that is, axis 14. In a preferred embodiment, a laser gauge is
utilized that locates the surface without contact with the thin
ceramic. Alternately, a mechanical instrument that contacts the
surface may be employed. The measurements are correlated with the
angle from reference direction 16 and the axial distance from an
end 15 and stored in a computer memory.
[0019] Following measurement of the surface, substrate 10 is
wrapped in a compressible mat 20 and inserted into a metal tube 22,
as shown in FIGS. 2 and 3. Mat 20 is formed of ceramic fibers and
provides thermal insulation of the substrate in the product
converter. Annular seals 24 are disposed about the substrate near
the ends to restrict gas flow through the mat.
[0020] The resulting wrapped substrate is coaxially inserted into
metal tube 22. Tube 22 includes a midsection 27 about substrate 10
and end sections 28 that extend axially beyond midsection 27. In
the preferred embodiment, tube 22 has an oval cross-sectional shape
similar to the substrate and is suitably sized to permit the
wrapped pre-assembly to be readily inserted.
[0021] Referring to FIG. 4, the pre-assembly of substrate 10, mat
20 and metal tube 22 is subjected to a spin-forming process to
reduce the tube radius of midsection 27 to secure the substrate
within the tube and form the catalytic converter. For this purpose,
the pre-assembly is mounted onto a chuck 26 that spins tube 22 to
rotate the tube about axis 14. While the tube is rotated, a
metal-forming tool 30 is radially urged against the outer surface
of the metal tube along midsection 27. In a preferred embodiment,
tool 30 is a roller mounted on a yoke 31 to rotate about an axis 32
parallel to axis 14. As roller 30 is radially urged against the
metal tube, the roller is concurrently advanced axially to
progressively reduce the tube diameter. As the diameter is reduced,
compressible mat 20 is compressed about substrate 10. In accordance
with this invention, roller 30 is connected to an actuator 34, such
as a hydraulic actuator, that positions the roller relative to axis
14, in response to a signal from a computer control module 36. A
suitable spin-forming machine is commercially available from
M&M Metal Forming Machinery, Inc., under the trade designation
Spin Shrinking Machine Model SSM 350 TT.
[0022] In accordance with this invention, the computer control
module determines the position of roller 30 based upon the radial
dimensions of substrate 10 measured prior to assembly within the
tube. As the tube spins about the axis, roller 30 traverses the
metal tube in a plane perpendicular to the axis. The computer
control module calculates desired radial dimensions for the tube
circumference in the plane by adding a predetermined radial
distance to the tube radial dimensions in the plane. Extrapolation
is used to calculate dimensions of the substrate in planes other
that those for which measured values are available. The computer
control module then positions the metal-forming roller to follow a
path corresponding to the desired housing dimensions.
[0023] In the final axial pass, tool 30 is positioned a radial
distance equal to the total of the substrate dimensions, the
desired thickness of insulation layer 43 and the thickness of
housing 42. In this manner, the method of this invention produces a
housing having an outer surface corresponding in shape to the
substrate and spaced apart by a uniform distance. Spin-forming may
be carried out in a single axial pass of tool 30. Alternately,
multiple passes may be used to incrementally reduce the dimensions
of the tube. In a process employing multiple passes, the distance
added to the substrate dimensions is preferably chosen to reduce
the dimensions of the tube a selected amount during each pass until
the desired final size is achieved
[0024] Following spin-forming of midsection 27 about the substrate
10, end sections 28 are formed into the desired size and shape of
the inlet and outlet for the catalytic converter. This is
preferably accomplished by spin-forming in a manner similar to the
process utilized for forming the midsection. The product catalytic
converter 40 is shown in FIGS. 5 and 6. Converter 40 comprises a
metal housing 42 that is formed by spin-forming in accordance with
this invention. Housing 42 includes a midsection 44 about substrate
10, with insulative layer 43 and seals 24 compressed therebetween.
Housing 42 also includes end portions 46 that form the inlet and
outlet to the catalytic converter. As can be seen in FIG. 6,
regulation of the metal-forming tool during spin-forming in
accordance with this invention produces a housing comprising a
midsection 44 having a shape corresponding to substrate 10 and
spaced apart by a substantially uniform distance. Moreover,
compression of mat 20 between midsection 44 and substrate 10
produces layer 43 having a substantially uniform thickness.
[0025] Therefore, this invention provides a method for forming a
midsection of a catalytic converter housing about a substrate
having a noncircular circumference. The metal housing conforms in
shape to the substrate and is uniformly sized about the substrate.
Moreover, the insulative mat is uniformly compressed about the
substrate to provide a uniform density within the housing
midsection.
[0026] In the embodiment shown in FIGS. 1-6, a method of this
invention was utilized in spin-forming a housing about a substrate
having an oval circumference. The method may be applied to catalyst
substrates having other suitable noncircular shapes, including a
race track circumference or a nonsymmetrical shape. In an alternate
embodiment, a housing is formed about a catalyst substrate that is
designed to be cylindrical but has a circumference that is
noncircular as a result of variations that occur during extruding
and firing of the ceramic, commonly referred to as out-of-round.
Referring to FIG. 7, there is shown an out-of-round catalyst
substrate 50 having a circumference 53 that deviates from a circle
52. In accordance with this invention, a housing may be spin-formed
about substrate 50 to correspond in shape to the substrate despite
the out-of-round deviations. This is accomplished by mapping
circumference 53 of the substrate prior to spin-forming to
determine the radial dimensions relative to an axis 54, which
corresponds to the central axis of the substrate as designed. The
substrate is wrapped in a compressible mat and coaxially inserted
within a metal tube. Thereafter, the substrate and metal tube are
spun about a center axis 54 while forming the metal tube with a
metal-forming roller. During forming, a control module adjusts the
position of the roller to follow a path corresponding to the actual
radial dimensions of the substrate plus a predetermined distance.
The product catalytic converter 56 is shown in FIG. 8 and comprises
substrate 50 surrounded by a layer 58 of insulative material and
enclosed within a midsection of a metal housing 60. The housing
midsection is out-of-round to correspond in shape to the
out-of-round dimensions of substrate 50. In addition, the housing
is sized greater than the substrate by predetermined distance to
provide a uniform layer 50 of insulation therebetween.
[0027] While this invention has been described in terms of certain
embodiments thereof, it is not intended to be limited to the
described embodiments, but only to the extent set forth in the
claims that follow.
* * * * *